This invention relates to a hip joint femoral prosthesis. More particularly, it relates to a prosthesis having fish scale depressions on the proximal end to enhance fixation after implantation, particularly in a non-cemented hip.
Femoral hip joint prostheses which have at their distal end a rod to be inserted into the femur medullary canal, and at the other end a neck made integral with an element for accommodating a femur head of spherical shape, are well known. Such prostheses have a shape to facilitate their introduction and positioning into a femoral intramedullary canal which has been previously reamed out by a surgeon. These prostheses must possess an outer surface permitting efficient regrowth of the bone tissue. Finally, the prosthesis must, as much as possible, be easily removable without causing any additional damage to the femur, since, obviously, the femur is already damaged to an extent requiring implantation of such a prosthesis.
In order for the femoral components to possess all of these properties, some of which are contradictory, it has already been proposed to give the rods a rectilinear shape or a shape presenting various curvatures with a circular or oval cross-section. These components may have a terminal angle that facilitates the introduction into, or the removal from the femur. These rods may also have flutes or serrations present at their periphery to permit better ingrowth of bone tissue; or they may even be coated with a coating layer known to be resorbed in the blood medium such as a hydroxyapatite layer.
However, a femoral component having such a coating thereon, which coating dissolves with time in the bone tissue, has a disadvantage. Due to dissolution of the coating, these components have a tendency to be driven more deeply into the femur. Such a displacement of the prosthesis with respect to the femur or bone in which it is implanted works against the firm anchoring of the latter in the canal.
It has been attempted to remedy this disadvantage by providing, on the walls of the proximal end of the femoral component, raised portions resisting any lowering of the prosthesis into the femur. In particular, these projections may be in the form of ladder steps or horizontal serrations. However, these projections are not entirely satisfactory because, as the area on which they might be made is limited, they fulfill their function only imperfectly.
U.S. Pat. No. 4,530,116 discloses an anchoring shank with a plurality of depressions having an arch-like shape with flanks which taper conically towards the proximal end. These depressions are intended to improve the adhesion between bone cement and the shank.